Receptacle overload switch



April 29, 1969 -K. M. DELAFRANGE E L RECEPTACLE OVERLOAD SWITCH Filed Dec. 20, 1965 United States Patent 3,441,799 RECEPTACLE OVERLOAD SWITCH Kenneth M. Delafrange, 96 Washington Ave., Westwood,

NJ. 07675, and Max Rappaport, River Edge, N.J.;

said Rappaport assignor to said Delafrange Filed Dec. 20, 1965, Ser. No. 515,043 Int. Cl. H02h 3/08 US. Cl. 317-9 6 Claims ABSTRACT OF THE DISCLOSURE A movable protection switch for preventing unnecessary delays and safety hazards in correcting domestic power overloads. A pivotable arm is maintained in a first position by natural magnetic attraction whereby the power circuit is uninterrupted. When an overload occurs, current flow creates an electro-magnetic field to pivot the arm to a second .position which breaks the circuit. After the overload is corrected, the arm can be manually reset to the first position.

This invention relates to circuit protection devices, and more particularly, to a circuit breaking overload switch adaptable for use in sockets and power receptacles.

In the past, difficulties have often been encountered with appropriately and yet economically protecting electrical systems against certain overloads, many of which are localized in nature. Protection devices designed with overload conditions in mind must operate definitely and rapidly to avoid the harmful effects of these overloads. That is, overloaded circuits must be broken almost immediately upon the occurrence of an overloaded condition in order to prevent damage to loads or machinery attached thereto; equally as important is the avoidance of wiring damage within walls, junction boxes, etc., due, for example, to wall socket overloads. It is certainly well known that many damaging fires are the result of poorly protected circuits which have become overloaded. All too often, some overload protection has been utilized in these circuits, but many of these protection devices have obviously proved inadequate.

There are numerous devices available for achieving circuit overload protection. However, these devices have not always struck a balance between adequate protection, economical manufacturing and developing costs, and compact packaging. Thus, many prior art circuit breakers involve complex electromechanical equipment which may be feasible for protecting large power users on a bulk basis, but which are not readily adaptable for use on a smaller scale, such as individual line sockets or receptacles. And although standard fusing and circuit breaking techniques can be applied to individual line use, the problems associated with such use are well known, i.e., groping in the dark for spare fuses and for the fuse box, the inability to locate a bad line leading to continuous and expensive blowing of the fuses or circuit breakers when the overload condition has not been rectified, etc.

What has too often been overlooked in the past is that provision must be made for localized overloading, as at a particular wall socket. Since one of the major causes of overloading is exceeding the current rating of an individual line by, for example, usage of too many appliances on that line, overload protection based on monitoring a plurality of coupled lines often does not act quickly enough to prevent serious damage.

It is therefore clear that a need exists for an inexpensive protective device which can be utilized on a per socket basis and which can furnish overload protection when a particular appliance or load at that socket creates the overload condition.

3,441,799 Patented Apr. 29, 1969 It is there-for an object of this invention to provide an improved overload protection device to obviate one or more of the aforesaid difficulties.

It is a further object of this invention to furnish such protection on a per socket or receptacle basis.

Another object of this invention is to achieve rapid and definite circuit breaking without complex circuitry.

One particular embodiment of this invention involves the use of a relatively small fully enclosed protection switch unit adaptable for use with, for example, a wall socket. The unit comprises 'a rod adapted to rotate about a pivot point within the unit structure. At one end of the rod is a contact point which normally makes with another contact point external to the rod. When these contacts are made or contiguous with each other, a power circuit is completed from a power input conductor to a small electromagnetic coil and thence to a power output conductor. When the rod is in this normal posi tion, a solenoid plunger projecting from the side of the rod is only partially thrust into the coil. This normal position is maintained by virtue of magnetic attraction between a small magnet at the other end of the rod and a first metallic stop mounted within the protection unit.

When an overload condition occurs, generally causing a heavy current flow, the coil which is directly in the line, develops a relatively strong electromagnetic field which serves to attract the plunger coupled to the rod. This attraction force is sufiicient to pull the plunger into the coil and thereby cause the rod to rotate about the pivot point after it has overcome the magnetic attraction between the magnet on the rod and the first metallic stop. When the rod pivots in response to the overload condition, the contacts mentioned above which had completed the power circuit between the first input and output conductors are physically separated, thus breaking the circuit.

When the circuit is thereby interrupted, the heavy current which resulted from the existence of the overload condition can no longer exist, and the magnetic field associated with the coil therefore collapses, As a result, there is no longer any significant attraction force applied to the plunger of the rod; however, due in part to the inertial rotational movement of the rod and also to the presence of a second metallic stop to which the rod magnet is attracted, the rod assumes a static second position which serves to keep the circuit contacts separated. Thus, the power circuit is definitely interrupted and none of the usual harmful and dangerous effects of excessive current flow can occur.

External indications of the condition of the overload switch are provided by means of an ionizable bulb connected across the input and output power conductors previously mentioned. When the circuit is operating normally and no overload condition is present, there is a complete circuit across the terminals of the bulb from the input power conductor through the closed contacts and the coil to the output power conductor. This represents such a low impedance path as to effectively represent no potential difference across the terminals of the bulb. Thus, the bulb remains extinguished. However, when an overload condition causes the rod to pivot and the contacts to separate, the potential across the leads of the ionizable bulb is arranged to be the full power applied to the circuit, limited only by suitable impedance means which are included for this purpose alone. Suflice it to say that this applied potential in the presence of an overload condition is quite suflicient to light the bulb and to provide an external indication that an overload condition exists with respect to this particular socket or line.

It has been indicated that the broken condition of the circuit will be maintained by the attraction between the rod magnet and the second metallic stop. The protective unit can be reset by means of a push button mechanism which is coupled to the rod. The push button itself protrudes, for example, through an orifice in the casing of the unit only when the rod assumes its second position in response to an overload condition. At all other times, the button is approximately flush with the casing. Thus, following an overload condition, the unit can be reset by simply depressing the push button which causes the rod to articulate about its pivot point in a direction opposite to that in which it moved in response to the overload condition. It moves until the rod magnet is attracted to the first metallic stop, at which time the power circuit is once again completed by the making of the contacts.

Assuming that the short circuit or overload condition has been remedied by this time, the power circuit will once again be fully operative. Of course, if the overload condition (i.e., an appliance short circuit) is still across the line, the resetting procedure will be ineffective, as the circuit breaking steps previously described will again occur once the circuit has been temporarily recompleted. As is well known in these circumstances, the actual cause of the overload must first be rectified before the power circuit can become fully operative once again. However, no costly or wasteful blowing of protective elements will occur in the interim.

It is therefore a feature of this invention that a compactly packaged device furnishes localized circuit overload protection.

Another feature of this invention is that a movable member overcomes a first magnetic attraction under the influence of a magnetic field developed in a coil in response to an overload condition.

A further feature of this invention includes resetting means for transferring said movable member to re-establish said first magnetic attraction to recomplete a power circuit by overcoming a second magnetic attraction.

A still further feature of this invention includes means for breaking a power circuit in response to the physical separation of contacts caused by the rotational movement of a pivoted rod, whereby a neon bulb is ionized in response to the contact separation to thereby indicate an overloaded condition.

The above brief description, as well as further objects, features and advantages of the present invention, will be more fully appreciated by reference ot the following detailed description of a presently preferred, but nonetheless illustrative embodiment demonstrating objects and features of the invention, when taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a front view of a socket or receptacle plate showing a dual socket with a protection device shown in phantom outline;

FIG. 2. shows the external wiring connections between the power input, the two female receptacles, and the protection device mounted behind the socket plate of FIG. 1;

FIG. 3 is an enlarged sectional view of the inner mechanism of the protection device, taken along the line 3--3 of FIG. 2; and

FIG. 4 is a combined electrical and pictorial diagram indicating the electrical equivalence of the protection device of FIG. 3.

One illustrative fashion in which the invention described herein can be utilized is shown initially in FIG. 1. There, a socket plate is shown to have facilities for dual plug-in operation at the female plugs 12 and 14. The hidden outline of a protection unit 16 is illustratively mounted behind the plate 10 in a vertical orientation. Of course, this is merely one illustrative positioning of the protection unit 16, and many other possible orientations can be visualized by those skilled in the art, e.g., a horizontal orientation between the two female plugs 12 and 14. Two orifices 18 and 20 are indicated in the socket plate 10 to allow for viewing the condition of a threshold indicating device and for a protruding reset mechanism respectively. These relationships will all become more clearly understood when the remaining figures of the drawings are taken into consideration.

Referring to FIG. 2, the wiring arrangement between the external power source (not shown), the sockets 12 and 14, and the protection unit 16 are indicated. Power is applied between conductors L and L The power circuit available to the female slots 22 of the socket 12 can be traced from power conductor L coupled to input terminal 32 of the protection unit 16, through circuit breaking elements to be described below coupled to terminal 34, and thence over upper output power conductor L to socket plate 24L at screw terminal 26U. The load is applied across the slots 22 and a continuous power circuit is traced therefrom to the socket plate 24R, the terminal 28U and the other input power conductor L With respect to the lower socket 14, the power circuit is identical as far as terminal 34, and proceeds therefrom over lower conductor L to terminal 26D of plate 24L. Following the load connected across slots 30 of socket 14, connection is made to plate 24R and via screw terminal 28D to input power conductor L In addition, the lower portion of power conductor L connects through terminal 28U and 28D to terminal 36 of protection unit 16 to complete an indicating circuit for the protection unit.

The actual operation of the invention can be explained when FIGS. 3 and 4 are considered together. Within the mounted casing of the unit 16 as shown in the enlarged sectional view of FIG. 3, taken along the line 33 of FIG. 2, are shown the three basic input terminals 32, 34 and 36, having connected thereto the power conductors L L and L respectively. Conductive rod 44 is pivoted at pivot point 46 and in its normal condition shown in solid outline in FIG. 3, it causes attached contact point 42 to make with externally fixed contact point 40. This serves to complete the monitored power circuit between power input conductor L and power output conductor L This can be followed by tracing the power circuit over and including the following elements: power conductor L terminal 32, lead 38, contact point 40, contact point 42, lead 58, terminal 60, coil 62, terminal 64, lead 66, terminal 34 and finally to power conductor L The rod 44 is maintained in its normal position when the load, connected across terminals 34 and 36, is drawing its normal load current. This, for example, may be as much as 20 amperes depending upon the load and the circuit parameters. This type of normal load current creates a relatively weak magnetic field around the coil 62, and although some solenoid pulling force is exerted on the plunger 48 attached to the rod 44, this force is insufiicient to overcome the normal position occupied by the rod, maintained by the attraction between the coupled permanent magnet 54 and the metallic stop 56R. Assuming, however, that an overload condition is presented to the unit by virtue of, for example, a heavy current drain due to a short circuit across terminals 34 and 36, the overall load current will instantaneously increase in response to this overload condition. For example, a normal load current of 20 amperes may suddenly rise to 60 or amperes. The damage which may be caused by this current increase must be almost as instaneously prevented by the circuit. This is achieved in the following manner.

When the load current rises rapidly in response to an overload condition, the magnetic field developed by the few turns of the coil 62 becomes rapidly stronger in a well-known manner. The electromagnetic pull thereby exerted on the plunger 48 attached to the rod 44 is arranged to be sufiiciently strong to overcome the magnetic attraction between the mounted magnet 54 and the stop 56R. Accordingly, the rod 44 rotates slightly in a clockwise direction about its pivot point 46. As soon as this occurs, the power circuit previously traced between conductors L and L is interrupted by virtue of the separation of contacts 40 and 42. This interruption of the power circuit immediately prevents the flow of the otherwise excessive current which could cause serious damage as heretofore described.

Since the current has been interrupted, the magnetic field associated with coil 62 now collapses. This eliminates the pulling force previously exerted on the plunger 48, but the rod 44 still has some rotational inertia which continues its rotational movement slightly. To insure that the rod 44 assumes a static position following an overload condition as previously described, the holding stop 56L is included and this serves to create another magnetic attracting force which causes the magnet 54 mounted on the rod 44 to adhere to stop 56L. The rod 44 thus assumes its relatively vertical static position shown in phantom outline in FIG. 3.

External indications that the overload condition is associated with a particular socket are given through the orifice 18 in the casing of the unit 16 itself. It is noted that an ionizable gas bulb, illustratively a neon bulb, is shown connected through its leads 68 and 72 between terminal 64 connected to one side of the coil 62 and to the fixed external contact 40. Normally, of course, in the absence of an overload, the rod 44 is positioned so that the power circuit is operative. The voltage drop between leads 68 and 72 under these conditions is very small, since there is a complete circuit of negligible impedance (through the coil 62) between leads 68 and 72. Thus, it is clear that under these normal conditions, the bulb 70 will not light.

However, when an overload condition occurs and the rod 44 rotates and contacts 40 and 42 are thereby separated, there is a significant potential difference across the leads 68 and 72 of the bulb 70. This potential is provided between power input conductors L and L over a circuit traceable from conductor L terminal 32, lead 38, contact point 40, bulb leads 72 and 68, terminal 64, lead 66, terminal 34, and via protective impedance 74 to terminal 36 connected to conductor L Protective imped ance 74 acts as a limiting impedance and may take the form, for example, of a resistor of illustrative value 47 kilohms. This serves to limit the current passing through the bulb 70 when the overload condition between terminals 34 and 36 was caused by a temporary current surge.

Of course, it is possible that the overload condition is the result of a short circuit between terminals 34 and 36 and that this condition still persists while the bulb 70 is lit. Thus, the impedance 74 would itself be short circuited. No problem is encountered under these conditions, however, since the bulb 70 can be selected to take a high voltage drop even in the presence of such an overload con dition. Thus, in addition to providing an external indication of the overload, the bulb 70 can act as a dropping impedance to limit the current How to the short-circuited load. As is Well known, such ionizable bulbs draw very small currents while nevertheless a relatively high voltage drop across its terminals.

The protection 'unit can be reset by transferring the rod 44 back to its initial normal condition whereby magnet 54 once again adheres to stop 56R. This can be achieved by the pressing of the illustrative pushbutton 20 which protrudes from the casing of the unit 16 in its overload position shown in phantom in FIG. 3. This horizontal motion is transmitted over member 52 to the rod 44 by means of illustartive pin and slot 50, and rod 44 is thereby rotated about its pivot point 46 to again resume its normal position. At this time, it can be seen from FIG. 3 that the pushbutton 20 is practically flush with the casing of the unit 16, thereby eliminating any unsightly effects which could result from a permanently protruding element.

When the unit is thereby reset, the contacts 40 and 42 are again made and the power circuit is once again completed. The renewed completion of the power circuit renders the circuit fully operative assuming, of course, that the overload condition has been rectified. If this is not the case, the completion of the circuit will only be temporary, with the circuit breaking operation previously de' scribed occurring again as soon as the contacts 40 and 42 are made. This serves to prevent further damages and yet still eliminate the often costly successive circuit breaking which occurs when the underlying cause of an overload condition is not immediately remedied.

It is to be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A protection device for preventing signal overloading of a power circuit comprising a control member movable between a first position and a second position, means for limiting the movement of said control member between said first and second positions, controlling means in controlling relation to said control member for initiating movement of said control member to interrupt said power circuit in response to an overload of said power circuit, magnetic means operable after said power circuit is interrupted to move said control member to said second position, conductive means coupled to said control member for completing said power circuit when said control member is in said first position and for interrupting said power circuit when said control member is in said second position, said controlling means including a coil connected in said power circuit and a plunger in projecting relation to said control member, whereby the movement of said control member from said first to said second position is initiated in response to the electromagnetic attraction between said coil and said plunger, overload indicating means connected between said coil and said conductive means and adapted to be energized in response to said overload of said power circuit, and resetting means coupled to said control member for transferring said control member from said second position to said first position.

2. A device in accordance with claim 1 including in addition a covering plate with at least two orifices, and wherein said indicating means includes a gas bulb visible through a first of said orifices and ionizable in response to the transfer of said control member from said first position to said second position, and wherein said resetting means includes a pushbutton adapted to reciprocate through a second of said orifices in response to the movement of said control member between said first and said second positions.

3. An overload protection switch for a power circuit comprising a first contact connected to one input side of said power circuit, a coil connected to one output side of said power circuit, a second contact for selectively coupling said one input side and said one output side of said power circuit through said first and said second contacts and said coil, switching means responsive to an overload condition between said one output side and a second input side of said power circuit for separating said first and said second contacts to break said power circuit, said switching means including a movable rod with said second contact afiixed thereto, a plunger attached to said rod and means for detachably positioning said rod in a first position whereby said contacts are contiguous and in a second position whereby said contacts are separated, whereby said contacts are separated to break said power circuit in response to the electromagnetic attraction of said plunger by said coil in the presence of said overload condition, indicating means connected between said first contact and said one output side of said power circuit adapted to be energized in response to the separation of said first and said second contacts, and a reset mechanism coupled to said rod for allowing transfer of said rod from said second position to said first position subsequent to said overload condition.

4. An overload protection unit comprising in combination an electrical socket including at least one power outlet, switch means transferr'able between .a first position and a second position for respectively completing and breaking a power circuit to said outlet, coil means responsive to an overload of said power circuit ,for initiating the transfer of said switch means from said first position to said second position, indicating means for generating an overload signal at said socket, and resetting means for returning said switch means from said second position to said first position.

5. An overload protection unit in accordance with claim 4 including in addition first and second stops foresstablishing said first and said second positions respectively, and an external contact connected to said power circuit, wherein said switch means includes a movable member, a contact mounted on said member selectively connectable to said external contact, magnetic means for furnishing selective attraction between said member and said first and said second. stops, and a shaft in solenoid relation with said coil means to provide electromagnetic attraction between said member and said coil means in response to said overload of said power circuit.

6. An overload protection unit in accordance, with claim 4 wherein said socket includes at least two orifices, and wherein said indicating means presents said overload signal throughthe first of said orfices and said resetting means reciprocates through a second of said orifices.

References Cited 'LEE HIX, Primary Examiner.

,R. V. ILUPO, Assistant Examiner.

US. Cl. X.R. 

